Bourbaki

Corollary 2

Tag 04BL, permanent. Cite it as [Bourbaki, Tag 04BL].

Commutative Algebra, chapter II, § 5. Finitely generated projective modules. Invertible fractional ideals

Every finitely presented flat module is projective.

If P is a finitely presented flat A-module and m a maximal ideal of A, the AmA_m-module P, is flat (§ 3, no. 4, Proposition 13) and finitely presented (§ 2, no. 4) and hence free (§ 3, no. 2, Corollary 2 to Proposition 5), Condition (b) of Theorem 1 therefore holds.

Remarks (1) There exist finitely generated flat modules which are not projective (Exercise 7). (2) Corollary 2 to Theorem 1 extends to modules over non-commutative rings (Chapter I, §2, Exercise 15).

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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Transcribed from the printed volume. Not translated.